Temperature controlled resistive-liquid dummy load

Abstract

A dummy load for a radio frequency transmitter uses a resistive liquid within a tube of non-conducting material as the load. The tube has grounded conductors at each end, and a centrally-located terminal that provides a load, with respect to ground, across two parallel branches. The output of the radio frequency transmitter is applied between the centrally-located terminal and ground. The ends of the tube are connected into a closed liquid loop that includes a temperature controlling system with a circulating pump, a heater for raising the temperature of the resistive liquid to a given, operating level, if necessary, and a heat exchanger for lowering the temperature of the resistive liquid to the given, operating level, when necessary; whereby the heat generated by the output of the transmitter can be dissipated, and the temperature of the resistive liquid, within the tube, kept at a constant mean temperature to provide a constant resistance under all load conditions.

I claim: 
     
       1. A resistive unit for a dummy load for a radio frequency transmitter comprising; a tube of non-conductive material having electrically-conducting end terminals on either end connected to a common ground; a centrally-located electrical terminal within said tube between said end terminals; a resistive fluid within said tube to provide resistances in parallel between said centrally-located terminal and ground; a radio frequency transmitter; means for applying the output of said radio frequency transmitter between said centrally-located terminal and ground; and means for controlling the temperature of said resistive fluid within said tube of non-conductive material, to maintain said resistive fluid at a given temperature, that will maintain a constant resistance between said centrally-located terminal and ground for all output loads of said radio frequency transmitter. 
     
     
       2. A resistive unit for a dummy load, as in claim 1, wherein said means for controlling the temperature of said resistive fluid within said tube comprises a temperature controlling unit for fluids connected in series with said tube, in a closed loop; said temperature controlling unit having a heater for warming said fluid, a heat exchanger for cooling said fluid; a pump for circulating said fluid through said tube and said temperature controlling unit; and temperature-sensitive means within said temperature controlling unit for actuating said heater or said heat exchanger to maintain the temperature of said fluid at a constant, given level. 
     
     
       3. A resistive unit for a dummy load, as in claim 1, wherein said tube of non-conductive material is bent in a "U" shape to place said electrically-conducting end terminals side by side on said common ground. 
     
     
       4. A resistive unit for a dummy load as in claim 2, wherein said temperature-sensitive means includes a first temperature sensor near one end of said tube; a second temperature sensor near the other end of said tube; means for connecting said sensors together, and means for establishing a mean temperature differential between said first and second sensors to control said heater and said heat exchanger to maintain said temperature at said given level. 
     
     
       5. A resistive unit for a dummy load, as in claim 2 wherein said heater is actuated by said temperature-sensitive means, if necessary, to bring the temperature of said resistive fluid up to said given level, and said heat exchanger is actuated, by said temperature-sensitive means, when necessary, to bring the temperature of said resistive fluid down to said given temperature. 
     
     
       6. A resistive unit for a dummy load, as in claim 2 wherein said heat exchanger is a radiator, through which said resistive fluid is circulated, said radiator having a cooling fan, actuated by said temperature-sensitive means, when necessary, to reduce the temperature of said resistive fluid to said given temperature. 
     
     
       7. A resistive unit for a dummy load, as in claim 2 wherein said given temperature for said resistive fluid is well above the ambient temperature, to increase the effeciency of said heat exchanger, but below the boiling point of said resistive fluid.